Plasterboard



Patented Mar. 18, 1952 'PLASTERBOARD, SCUFF RESISTANT PAPER LINER, ANDPROCESS Harry N'. Huntz'icker and John K. Wise, Evanston,

'Ill., assignors to United States Gypsum Com.-

pany, Chicago, 111., a corporation of Illinois No Drawing. ApplicationJune 22; 1948, Serial No. 34,555

6 Claims.

This invention relates to scuff resistant paper and a process forproducing same and more particularly to a building element, such asgypsum wallboard, having scuff resistant'paper applied to one surfacethereof. I

Processes and apparatus for the manufacture of gypsum wallboardincluding a set-hardened gypsum core between a pair of paper liners arewell known inthe art. One such process comprises the steps of covering ahigh rosin size paper sheet with an aqueous slurry of gypsum to apredetermined depth, applying thereover a second paper sheet, and thenpermitting the slurry to set. The gypsum may contain a small quantity ofstarch which assists in the formation and maintenance of a strong bondbetween the paper sheets and the gypsum core in the final product. Afterthe gypsum has set, the board iscut to size and kiln dried.

Gypsum wallboards prepared as indicated above are standard articles ofcommerce and are sold in large quantities. These boards are customarilyerected bynailing them to conventional wood studs. However, in buildingconstruction, the joints between successive boards, that is, the placesat which an edge ofone board abuts against a correspondingedgeof'anotherboard, have a tendency to be unsightly in the finished wall.Many different methods have been attempted. in aneffort to provide acheapyfeasible means of rendering the joints invisible in the final wallstructure. The most widely used method has been to cover the joint witha filled aqueous adhesive cement, usually of the protein type, and embedtherein a paper tape. After the adhesive cementhas dried,.an additionalcoat of the same or another adhesive is applied to smooth ofi thecompleted assembly. When this last mentioned adhesive has dried, thecemented area, which usually extends over each board face for. severalinches :on either side of the joint, is sanded smooth. The result is asmooth, level, monolithic wall construction which is ready to bedecorated.

The above mentioned system of Wall construction has certaindisadvantages when employing paper-lined plasterboards that are nowavailable in commerce. When the final coat of the joint cement issanded, it is; practically impossible for the mechanic to avoid touchingand sanding the adjacent paper surfaces ofthe wallboard with thesandpaper. Wherever suchcontact occurs, .the surface of the paperof-the--wallboard is scuffed. This is very undesirable since subsequentpainting tends to accentuate rather than to, cover the scuff marks. Afurther undesirable feature is that the paper surface of the Wallboardexhibits, when painted with oil paints, a marked QThis. also causes anunsightly appearance.

Factory sizing of1finished'plasterboardsz. is impractical because thecost of handling the boards would be prohibitive. Furthermore,plasterboards emerge from the dryingkilns at such a high rate of speedin lineal feet per-minute that equipment necessary to size them atthispoint in the operation would be prohibitive in cost. The obviousexpedient of applyingxaconventional size coat to the paper'before theboard is'formed has proven to be a practical'impossibility.. This is sosince at least a part of the water. present in the initial aqueousplaster slurry mustr be removed from the core during the drying.operation, thus necessitating that the I vapors pass directly throughthe paper liners For this reason the porosity of the paper must be veryclosely and carefully controlled prior to and during manufacture of theplasterboard. Experience has shown that application of conventional sizecoatings to the paper tends to seal-the sheet' and render it lessporous. Thus when a gypsum wallboard is made from such a sheet, thewater vapor in the core will have a tendency to blow the paper loosefrom the core during the drying cycle.- in the kilns. v It is,thereforeone object of this invention to provide .an inexpensive, easyto apply. sizing material capable of imparting to gypsum wallboard paperresistance to scuffing and fiber raising without substantially changingthe porosityof the sheet.

A further object of this invention is thetprovision of a porous papersheet having scuff resistant properties which is particularly useful inthe manufacture of paper-lined gypsum boards.

A further object of this invention isthe provision. of a processofpreparing paper having increased scuff. resistance without impartingexcessiveembrittlement properties to the. paper.

A still further-object. of this invention is the provision of apaper-lined building element, such as plasterboard, which is. resistantto scuffing when treated with sandpaper and which iscapable ofdecoration, even on the sanded portions, with oil paints orwater-thinned. paints. without bleeding or other adverse effect.

Further andadditional objects. will appearfrom the following description.and .theappended claims.

. In accordance with this invention it has been discovered that scuffresistant properties may be imparted to paper by treating a paper sheetwith a product prepared by heating together Water, a polysaccharide fromthe group consisting of starches and dextrins, an aliphatic aldehyde anda nitrogen compound capable of reacting with the aldehyde to form aresin or the amine-aldehyde type. In accordance. With'one embodiment ofthis invention, an aqueousdispersion of starch or dextrin is. heated,preferably abovexthesgelat- 3 inization temperature, in the presence ofurea and formaldehyde to form a reaction product which is thereafterused to treat a paper sheet, as will be hereinafter more fullydescribed. The nature of the reaction between the starch or dextrin andthe urea and formaldehyde is not clearly understood and it is notdefinitely known whether a well defined chemical reaction productactually forms during this heating treatment. However, it has beendiscovered that the heat treatment of these substances together inaqueous solution is necessary prior to the time that the solution isapplied to the paper whereby to produce a paper having the desired scuffresistant properties and porosity. Simple mixtures of starch or dextrinand a previously formed urea-formaldehyde resin applied to a paper sheetexhibit insufficient penetration into the sheet, excessive embrittlementof the sheet, and markedly reduced porosity. Likewise treatment of apaper sheet with unreacted starch, urea and formaldehyde does not givethe desired penetrability or the necessary degree of porosity that areobtained by the process and product disclosed and claimed herein.

In order more fully to explain the invention, reference will be made tothe following examples which illustrate several particular embodimentsthereof. However, it will be clear to one skilled in the art that thisinvention is not to be limited by the examples given but only by thescope of the claims appended hereto.

Example 1 The following ingredients in the amounts indicated in parts byweight were thoroughly mixed:

Dextrin 120 Urea 40 Formalin (37%) 216 Water 290 The acidity of theresulting solution was adjusted to pH 5 to 5.5 and the batch was heatedto 85? C. and held between 85 and 90 C. for minutes. Thereafter theacidity was adjusted to about pH 7 and the heating continued for an additional 45 minutes. The resulting solution containing the reactionproduct or condensate of dextrin, urea and formaldehyde was applied inseveral concentrations (by diluting with water where necessary) to onesurface of a chip paper of the type ordinarily employed in making gypsumwallboard. This paper was a highly rosin sized paper. The excesssolution was then removed by a doctor blade and the sheet dried. Thedried sheet was then baked to cure the condensate contained thereinunder conditions which simulate the high temperature drying ofplasterboard in a commercial manufacturing process, minutes at 250 F.being adequate. The resulting sheet was found to be remarkably resistantto scuffing and fiber raising when sanded with paper or emery cloth.Tests were made on the several papers with the results indicated in thefollowing table:

The porosities reported in this example and in the succeeding exampleswere determined ac- -cording to the standard Tappi method T-460m-44.

The porosity values refer to the number of sec onds for cc. of air topass through a porous sheet under standard conditions. Accordingly thelower numbers in the table indicate a higher porosity.

Example 2 The following ingredients in parts by weight were thoroughlymixed:

Oxidized starch 40 Urea 30 Formalin (37%) 162 Water 168 Per cent Percent Solids in ggg gg' g Condensate treating solution 5 9 re in final t1eatment treatment sheet 25 s 170 260 Z. 8 185 190 1. 5 160 160 l. 2

Although the porosity of the sheet treated with the 25% solutiondecreased from 170 to 260, this latter value is still well within therange required for gypsum board paper. The sheets were highly resistantto scuffing and fiber raising.

Example 3 The following ingredients in parts by weight were thoroughlymixed:

Dextrin 90 Urea 5 Formalin (37 27 Water 278 Per cent Per cent Solids inff g Condensate treating solution S as e ore ee er in final treatmenttreatment sheet The sheets were found to be resistant to scuiiing andfiber raising.

Example 4 The following ingredients in parts by weight were thoroughlymixed:

Starch (90 fluidity) Urea 40 Formalin (37%) 216 Water 580 The acidity ofthe mixture was adjusted-to pH 5 to 5.5 and it was heated at 85 to 90 C.for one hour. Thereafter the acidity was adjusted mea ow 25? CI. Thesolution is stirred. for three minutes andiallowed to stand forf27'minutes, after'whi'ch the. volume of solution which-flows from astandard orifice. in 70 seconds at 25 C. is measured. This volume isregarded as the fluidity of the starch (see Kerr; Chemistry and"Industry of Starch, 1944, at page 95).

Example In this example the following ingredients in parts by weightwere employed:

Acid hydrolyzed cornstarch of 90 fluidity; 150

Urea 40 Formalin' (37%) 216 Water Q. 580

Asmooth paste was formed of the starch with some. of the water and.thereafter the remaining ingredients were added thereto in the amountsspecified. .The acidity was adjusted to pH 4.9 with dilute aceticacidand the batch washeated with stirring to 85 to. 90 C. and held at thattemperature for 60 minutes. Thereafter the acidity .wasadjusted to aboutpH 6.6 and the'heating was continued for another 60 minutes wherea-fterthe batch was allowed to cool. A portion of the resultingcondensatewasapplied to a piece; of

high rosin size'chipboardpaper. 'After removal of the excess of thecondensate by a doctor blade and baking, the surface of the sheet wasfound to be highly resistant to scuifing when rubbed with sandpaper oremery cloth. As a matter of fact, the abrasive actually smoothed ratherthan roughened the surface. The porosity and flexibility of the sheetwere changed only slightly.

Another portion of the condensate formed as above indicated in thisexample was acidified to pH .4with alum. This acidified solution wasappliedto another piece of chipboardpaper. in the manner indicated abovewith substantially the same results. A film cast from the acidifiedsolution became hard and insoluble in water upon baking.

Example 6 The following ingredients in parts by weight The acidity wasadjusted to pH'5.2 with acetic "acid and sodium hydroxide. heated forone hour'at' 85 to 90C. whereafter the acidity'was adjusted to pH7.44With sodium hydroxideand the heating continued for an addi-- Thebatch was tional hour." Chipboard paper treated: with the condensate inthe manner previously indicated was foundto be highly resistant toscuffing and fiber raising. and the porosity of'the paperx'wassubstantially unchanged; The condensate inzthis example. penetrated the:paper. a, 1 little .more readily than; the: condensate of. Example 5.

' Example 7 a l-he. following. ingredients in: parts by weight weremixed together:

Oxidized starch. Urea 5 "10 Formalin (37%) "-27 Water 685 The resulting.mixture hadan unadjusted acidity of pI-I 7.8. It was heated for one hourat to C. during which time theacidity drifted to pH 6.74. When. appliedto chipboard paper in the manner previously indicated, .this condensategave excellent sculi resistance with little change in sheet porosity.

Example 8 .The following ingredients in parts by weight were mixedtogether:

Dextrin 50 Urea 30 Formalin (37 92 Water 400 The mixture was heated for90 minutes at 85 to. 90 C'., the acidity being about pH 6. Thecondensate was applied ,to. paper in the manner previously indicatedandwhen the excess was removed and the sheet baked, it showed excellentscuff resistance and. partioally .no change in porosity.

Example 9 The following ingredients in parts "by weight were mixedtogether:

Enzyme converted starch Urea '75 .Formalin (37%) 200 Water 700 Theacidity of the resulting batch was adjusted to. about. pH 7 and thebatch was then heated for two hours at 85 to 90. C. Paper treated withthis condensate and baked was resistant to scuffing and substantiallyunchanged in porosity.

It will be apparent from the foregoing examples. that the amount ofcondensate applied to the surface of the paper may vary within widelimits. It is preferred, however, that the conditions be controlled sothat the final paper sheet product contains between about 0.5 and about5.0 per cent by weight of condensate, preferably between about 1.0and.3.0 per cent. It is pre ferred for proper porosity control that thecondensate penetrate into the surface of the sheet at least to someextent. Penetration may be expedited by rolling or calendering thesheet. Obviously the bulk of the condensate is close to the surface andin the case of manila papers the manila liner may contain 35 per cent orso of.

sheet onecalendermg. However; it: wi1'l :-be.apparent that the other;methodsiof: application .will occur to those. skilled in the, art.

analogous fashion with aldehydes.

I'he paper that has been treated in the manner indicated in the previousparagraph is ready for application as aliner to ypsum board. This may beeffected in any desired manner such as those commonly in practice now inthe industry and as indicated in the foregoing. After the paper-linedgypsum sheet has set, the gypsum board is then dried out in suitablekilns maintained at high temperature. The heat treatment in the kilnsserves in a measure to bake or cure the condensate directly within thepaper sheet, thereby rendering the sheet scuff resistant. Thiscorresponds to the baking step indicated in the previous examples. It isat this point in the manufacture of the gypsum board that it is mostdesirable for the porosity of the paper sheet to be maintained since inthe drying kilns or ovens water vapor must escape through the paperliners. If the liners are insufiiciently porous, then they will have atendency to be blown loose from the gypsum core during the drying cycle.In the commercial kilns now in use, the air intake temperature may rangebetween 250 and 500 F. and accordingly the paper liners must permit ofthe ready escape of steam or water vapor therethrough during the dryingperiod.

As previously indicated, it is an important feature of this inventionthat the polysaccharide (i. e. starch or dextrin) be heat-treated in thepresence of water and the urea and formaldehyde prior to application tothe paper sheet. In connection with this cooking procedure, there do notappear to be any critical factors other than those which will permit theproper reaction between the several ingredients to take place. As iswell known in the resin art, the speed and extent of reaction willdepend upon the interrelationship of time, temperature, acidity andconcentration factors. However, it is preferred to heat or cook theseveral ingredients at a temperature which is above the gelatinizationtemperatures of the starch or dextrin employed. The range of 85 to 90C., as indicated in' all of the examples, is suitable. As previouslyindicated, if the several ingredients are not precooked or otherwiseprereacted prior to the time that they are applied to the paper, it issubstantially impossible to obtain proper penetration. The preheating orprereacting of the several ingredients breaks down the gelcharacteristics of the starch or dextrin, and a viscous flow ispermitted'which'will permit at least a portion of the composition topenetrate into the surface of the paper.

It will be apparent from the foregoing that any type of starch ordextrin may be employed in accordance with this invention. It ispreferred to usea converted starch to improve penetration so that theproper amount of condensate will be carried into the sheet. Aspreviously indicated, the amounts of condensate present in v. the finalsheet may be as high as 5 per cent of the total weight of the sheet, thepreferred range being between about 1 and 3 per cent. It will also beapparent that the urea may be replaced in whole or in part with othernitrogen-containing organic compounds known to react in an Suchmaterials may include thiourea, melamine, dicyan- -diamide, biuret,formamide, acetamide ethanoI- amine, diethylamine, sulfamates and thelike. As a matter of fact, while urea is preferred, any amine or amidemay be employed which is capable of reacting with an aldehyde to form aresin commonly referred to as one of the amine-alde hyde type. Likewisethis invention is not limited to the use of formalin as specified in theforegoing examples. Other sources of formaldehyde, such asparaformaldehyde, trioxymethylene, hexamethylenetetramine, etc. may beemployed. Also other aldehydes which may react with the amine and/oramide, such as acetaldehyde, butyraldehyde, glyoxal, furfural, etc. maybe employed as complete or partial replacements for formaldehyde.

As will be apparent from the foregoing examples, the treated paper maybe prebaked' to set the resin and thereafter the paper may be applied toa gypsum board as a top cover sheet.

While several particular embodiments of this invention are shownabove,it will be understood, of course, that the invention is not to belimited thereto, since many modifications may be made, and it iscontemplated, therefore, by the appended claims, to cover any suchmodifications as fall within the true spirit and scope of thisinvention.

We claim:

1. A decoratable plasterboard having secured to at least one surfacethereof a porous, highly sized calendered paper sheet havingscuff-resistant properties, said sheet containing in graduallydiminishing quantities from the exposed surface thereof in an amountbetween about 0.5

and about 5 per cent by weight of the sheet, a heat-cured pre-formedheat reaction product of water, a polysaccharide selected from the groupconsisting of starches and dextrins, a compound selected from the groupconsisting of aliphatic amines and amides, and an aldehyde, the molarratio of said aldehyde to said compound being within the range of abouttwo to one and about four to one. 7

2. The plasterboard recited in claim 1 wherein said compound is urea andwherein said aldehyde is formaldehyde.

3. A porous, highly sized calendered paper sheet suitable for use as agypsum wallboard paper liner and having scuff-resistant properties whichcontains in gradually diminishing quantities from one surface thereof inan amount between about 0.5 and about 5 per cent by weight of the sheet,a, heat-cured pre-formed heat reaction product of water, apolysaccharide selected from the group consisting of starches anddextrins, a compound selected from the group consisting of aliphaticamines and amides, and an aldehyde, the molar ratio of said aldehyde tosaid compound being within the range of about two to one and about fourto one.

4. The porous paper sheet recited in claim 3 wherein said compound isurea and wherein said aldehyde is formaldehyde. Y

5. A process of treating a highly sized porous paper suitable for use inthe manufacture of paper-lined gypsum wallboard to impart scuffresistantproperties to said paper without essentially changing the porositythereof which comprises applying to one surface of said sized paper anaqueous solution of a heat reaction product of water, a polysaccharideselected from the group consisting of starches and dextrins, a compoundselected from the group consisting of aliphatic amines and amides, andan aldehyde, the molar ratio of said aldehyde to said compound beingwithin the range of about two to one and about four to one, the amountof said solutionapplied to said paper being sufficient to deposit onsaid surface solid'reaction product 9 in an amount equal to betweenabout 0.5 and about 5 per cent by weight of said paper, and thereaftercalendaring said paper whereby said reaction product is distributed inthe paper in a gradually decreasing concentration from the surfacethereof.

6. The process recited in claim 5 wherein said compound is urea andwherein said aldehyde is formaldehyde.

HARRY N. HUNTZICKER. JOHN K. WISE.

REFERENCES CITED UNITED STATES PATENTS Name Date Bauer et a1 Aug. 20,1940 Number 10 Number Name Date 2,246,635 Moller June 24, 1941 2,338,602Schur Jan. 4, 1944 2,352,553 Lefebure June 27, 1944 2,452,054 Jones Oct.26, 1948 2,496,440 Caesar et a] Feb. 7, 1950 FOREIGN PATENTS NumberCountry Date 539,331 Great Britain Sept. 5, 1941 57,967 Netherlands Aug.15, 1946 OTHER REFERENCES The Use of Urea-Formaldehyde Resin forWaterproofing Starch Used in Corrugated and Solid Fiberboard Production,by Philip B. Taft, published in the Paper Trade Journal, Oct. 15, 1942,pages 30-32 or Tappi Sections 206-208.

